The present invention relates to a semiconductor memory device and a manufacturing method therefor, and more particularly, to a capacitor in a semiconductor memory device, which has electrodes including a silicon carbide layer, and a manufacturing method therefor.
Each cell of a semiconductor memory device, e.g., a DRAM device, has a capacitor for storing information, and to ensure the accurate reading out of the stored data, the capacitance of the capacitor should be sufficiently large. Recent advances in integration technology, have led to increased integration by a factor of four, while typical DRAM chip area has only increased 1.4 times. This translates to a one-third relative reduction in the area of a memory cell. Therefore, since capacitor structures must be improved to obtain a larger capacitance within a smaller area, either the dielectric film's thickness must be reduced, the capacitor's effective area must be increased or a material having a higher dielectric constant must be used. The present invention relates to the third method for improving capacitance.
Conventional dielectric films include silicon dioxide (SiO.sub.2), silicon nitride (Si.sub.3 N.sub.4), or a combination thereof i.e., ONO (SiO.sub.2 /Si.sub.3 N.sub.4 /SiO.sub.2) or NO (Si.sub.3 N.sub.4 /SiO.sub.2) structure. These materials, however, have rather low dielectric constants, so that a complicated three-dimensional storage electrode is required for the next-generation of DRAM devices. Alternatively or the thickness of the dielectric film must be dangerously thin. To avoid these problems in DRAM capacitors, high-dielectric materials, e.g., Ta.sub.2 O.sub.5 or TiO.sub.2, and ferroelectric, e.g., SrTiO.sub.3 (STO) or (Ba, Sr)TiO.sub.3 (BSTO) and paraelectric materials, have all been suggested for use as the dielectric film, in which case it is preferable that titanium nitride (TiN), a composition layer of TiN and polysilicon, or tungsten be used as the material constituting the electrodes.
In such cases, however, subsequent heat-treatment or Boro-Phosphorus Silicate Glass (BPSG) deposition/reflow processing activates the oxygen atoms of the dielectric film, so that they combine with the capacitor electrode material, thus increasing the equivalent oxide thickness of a dielectric film and generating leakage current. Particularly, should the capacitor electrodes be formed of TiN, oxygen atoms combine with the electrode material when forming the dielectric film under an O.sub.2 atmosphere, to thereby form TiO.sub.2 on the interfaces of the capacitor electrodes and dielectric film, and an underlayer may become oxidized by the diffusion of oxygen atoms through TiN grain boundaries. Furthermore, should the underlayer be formed of polysilicon, a SiO.sub.2 film is generated between the TiN and polysilicon, to thereby result in increasing the equivalent oxide thickness of a dielectric film. Meanwhile, should the dielectric film be formed of STO or BSTO, platinum is generally used for the capacitor electrodes to prevent the oxidation thereof, but cannot be well etched when etching for its low vapor pressure.
Therefore, when the dielectric film of the next-generation DRAM capacitor is formed of an insulating material having a high dielectric constant, a ferroelectric material, or a paraelectric material, the capacitor electrodes should be formed by a material which exhibits excellent resistance to oxidation, can be simply etched and can prevent oxygen atoms from being diffused through a grain boundary.